In recent years liquid crystal display devices are widely used for digital display in table electronic computers, electronic clocks, etc., or for analog display in measuring instruments, electronic instruments for domestic use, acoustic instruments, etc. In particular, recently there is an increasing demand for coloration of display by liquid crystal display devices used in the terminal devices of various meters and instruments in an automobile, telephones and television receivers. To meet the demand there have been proposed various color liquid crystal display devices. some of which have already been put to practical use.
Examples of known color filters adapted for use in liquid crystal display devices to enable color display are as follows:
A. The one which comprises a transparent substrate on the inner surface of which a gelatin layer is formed and colored with acid dye.
B. The one which comprises a transparent substrate on the inner surface of which a layer of nitrogen-containing resin capable of being colored is formed and colored with acid dye.
C. The one which comprises a transparent substrate on the inner surface of which a transparent electrode is first formed and a color layer is formed by electrodeposition with the transparent electrode used as a plating electrode.
These filters, however, have disadvantages such as follows:
Since the color filter A is not resistive to heat, cracks are produced by application of heat necessary for formation of a transparent electrically conductive film on the color filter by vacuum evaporation. If the vacuum evaporation is conducted at low temperature, the transparent electrically conductive film will have a high electrical resistance or a low transmittance. Since the filter is not resistive to water, it is difficult to rinse it with an aqueous solution, and the display function of the liquid crystal is lowered by dirt.
Since the color filter B is not resistive to heat, either, as in the case of the above-mentioned color filter, cracks are produced by application of heat necessary for formation of a transparent electrically conductive film by vacuum evaporation. If the vacuum evaporation is conducted at low temperature, the transparent electrically conductive film will have a high electrical resistance or a low transmittance. There is also a problem that the resin is decomposed, colored or melted. Even in the temperature range where no such problem arises, there is also a danger of occurrence of what is called bleeding, that is, a phenomenon that the dye that has formed a particular pattern is caused by the heat to migrate into those areas where it should not, thereby to cause mixing of colors.
In both the color filters A and B, since the dyeing is conducted by photolithography, the manufacturing process is complicated and the cost is high. When a pattern of more than two colors is to be formed, it is impossible to form component parts of different colors on the same plane, and it is impossible to make thick layers, with resulting difficulty of dyeing at high density.
In the color filter C, since the color layer is formed by electrodeposition, the number of the kinds of dyes or pigments that can be used is small, so that there is a limitation to the kinds of colors that are available for dyeing.